Being in a primary relationship is believed to result in logistic and emotional support that provides health- promoting benefits. However, in a recent report of adherence to antiretroviral therapy (ART) among a large diverse sample of adults living with HIV, we detected a counterintuitive association in two separate samples between being in a primary relationship and worse adherence to medications. Such findings raise the question of how relationship dynamics impact adherence to HIV treatment. The purpose of the proposed study is to investigate, through qualitative and quantitative methods, the relationship factors that are associated with adherence to ART. The proposed study will be conducted in 3 phases. Based on recruitment feasibility and the epidemiology of the HIV epidemic in the San Francisco area, we will include HIV+ seroconcordant and serodiscordant male couples. Phase 1 will be a qualitative investigation of relationship dynamics and partner tactics related to adherence. Phase 2 will be the development of a medication adherence-specific measure of partner support, and will include specific tactics informed by Phase 1. Phase 3 will be a cross-sectional study of 300 couples which will (a) validate the adherence specific measure of partner support constructed in Phase II;and (b) test specific hypotheses of the inter-relationships among individual variables (e.g., quality of life, psychological well being, substance use) and couple-level variables (e.g., relationship satisfaction, conflict, adherence specific partner support), and ART adherence and clinical variables. Adherence to ART will be measured by 2 validated self-report measures. Clinical status will be assessed by viral load and CD4 count. All phases will be guided by social control theory and findings will have clinical implications for the development of interventions to improve adherence within couples and theoretical implications for understanding the role of social control in HIV treatment adherence.